Associate laboratory



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Thematic Area D: Signal Processing in Communication Networks and Multimedia




1- Summary of activities



Action 1 – Signal Processing for Wireless Communications Radio Systems

(i) - Blind source separation

Under a Bayesian framework and resorting to some differential-geometric based techniques in Random Matrix Theory, we incorporate the pdf of the residual unitary matrix to develop the joint MAP channel/source estimator. To implement our estimator we developed geodesic descent optimization algorithms to quickly locate the missing unitary channel factor within Lie group of unitary matrices.

Regarding the joint source symbol detection and multi-channel acquisition problem, in the context of wireless digital flat-fading links in SDMA architectures, our approach relies on a statistical model which decouples the time dynamics of the multi-channel vector in amplitude and direction. Preliminary results assess that our channel model approximates the statistical behaviour of certain well-known wireless channels even in the presence of Doppler spread. Computer simulations confirm that the developed differential-geometric based methods outperform the traditional optimization schemes.

(ii) - Space/time coding

In nonchoerent communications, channel estimation based on 2nd order statistics (SOS) is ambiguous, i.e., certain members of the parametric statistical family are locally undistinguishable and the Fisher information matrix is singular. Fundamental limits for the intrinsic variance of unbiased estimators in parametric estimation problems with a priori deterministic constraints were derived, based on a Riemannian geometric perspective.


Action 2 – Underwater Acoustic Communications Systems


(i) - Multicarrier communications

When compared with other approaches, our receiver structure provides a direct extension of known single-carrier/single-user results based on decision-feedback equalization, thus retaining the ability to handle severe multipath distortion.



(ii) – Physics-based signal processing

Time-reversed focusing by using multiple transmit/receive elements is a means of reducing the effects of ISI in digital communication signals, including OFDM-modulated waveforms. When the number of available transducers is insufficient to properly focus the desired OFDM waveform, MIMO equalization was shown to be a suitable receiver structure.



(iii) – Software-defined radio

The basic software functionality for a real-time single-carrier modem has been completed. This includes packet generation (framing), error-correction coding, equalization and timing and carrier recovery.



Action 3 – Acquisition of 3D Models of Real Environments

(i) – Automatic Modeling of Architecture

Steps towards reliable image based tracking and matching processes, together with observer motion estimation, were obtained at the level of image to image matching on one side, and motion estimation without correspondences on the other side. It is then possible to create a 3D model of a scene using pairs of images, and to estimate camera motion (orientation), provided the environment has some structure.



(ii) – 3D Modeling from Video

A tool for coding video using 3D representations was developed relying, essentially, on the possibility of reconstructing a scene from partial views. Both the complexity and the computational issues were not addressed yet.



2- Indicators





 

Area D

Publicações

 

Books (editor)

 

Books (Chapters in books)

1

Papers in International Journals

5

Papers in National Journals

 

Communications in Conferences

 

In international conferences

6

In national conferences

 

Reports

 

Organização de Seminários e Conferências

2

Advanced Training

 

Ph.D. Thesis (concluded)

1

M.Sc. Thesis (concluded)

2

Others

 



3- Publications

In Book (1)


Pedro M. Q. Aguiar, Radu S. Jasinschi, José M. F. Moura, and Charnchai Pluempitiwiriyawej, Content-based Image Sequence Representation, in Digital Image Sequence Processing, Compression and Analysis, CRC Press, August 2004.

In international journals (5)


André T. Martins, Pedro M. Q. Aguiar, and Mário A. T. Figueiredo , Orientation in Manhattan: Equiprojective Classes and Sequential Estimation, IEEE Transactions on Pattern Analysis and Machine Intelligence, 2004 (accepted for publication).

Pedro M. Q. Aguiar and José M. F. Moura, Figure-Ground Segmentation from Occlusion, IEEE Transactions on Image Processing, 2004 (accepted for publication).

J. Buescu, A. C. Paixão, F. M. Garcia and I. M. G. Lourtie. Positive-Definiteness, Integral Equations and Fourier Transforms. In Journal of Integral Equations and Applications, vol. 16, no. 1, Spring 2004.

F. M. Garcia and I. M. G. Lourtie. Detection of Transient Signals with Unknown Localization. In IEEE Signal Processing Letters, vol. 11, no. 9, September 2004.

P. Lopes, J. Xavier, V. Barroso, Blind Source Separation and Channel Identification: Exploiting 2nd Order Statistics in Bayesian Frameworks, Journal of the BrazilianTelecommunications Society (JTBS).

Papers in international conferences (6)


Bruno B. Gonçalves and Pedro M. Q. Aguiar, Complete 3-D models from video: a global approach, IEEE International Conference on Image Processing ICIP'04, Singapore, October 2004.

Bernardo Esteves Pires and Pedro M. Q. Aguiar, Registration of images with small overlap, IEEE International Workshop on Multimedia Signal Processing MMSP'04, Siena, Italy, September 2004.

J. Xavier and V. Barroso, The Riemannian Geometry of Certain Parameter Estimation Problems with Singular Fisher Information Matrices, IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP'04), vol. 2, pp. 1021-1024, Montreal, Canada 2004.

J. Xavier and V. Barroso, Geodesic Lower Bound for Parametric Estimation with Constraints, IEEE Signal Processing Advances on Wireless Communications (SPAWC’04), Lisbon, Portugal 2004.

J. Gomes, V. Barroso. "MIMO Decision-Feedback Equalization with Direct Channel Estimation." in Proc. 5th IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC'04), Lisbon, Portugal, July 2004.

J. Gomes, V. Barroso. "Time-Reversed OFDM Communication in Underwater Channels." in Proc. 5th IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC'04), Lisbon, Portugal, July 2004.



Organization of Seminars and Conferences (2)




SPAWC –5th IEEE International Workshop on Signal Processing Advances for Wireless Communications
Instituto Superior Técnico, Lisboa, Portugal, 11-14 July, 2004 http://spawc2004.isr.ist.utl.pt/

SPAWC-2004, the fifth IEEE International Workshop on Signal Processing Advances for Wireless Communications, was devoted to recent advances in signal processing for wireless and mobile communications. This workshop brings together members of the signal processing, communications and information theory communities, working in universities, research centers and telecommunications companies. The meeting featured keynote addresses by leading researchers, as well as invited and contributed papers.



SPAWC-2004 was held at Hotel Tivoli - Tejo, in Lisbon, Portugal, more precisely at the Parque das Nações. This site offers some of the most daring examples of contemporary architecture, Europe's largest Oceanarium, delightful thematic gardens, exhibition centers, theaters and event halls, all located along a breathtaking 5 km stretch of the Tagus riverfront, in the heart of Lisbon, benefiting from a wide array of shops, restaurants and bars. Only five minutes from Lisbon International Airport, Parque das Nações builds on the heritage of EXPO'98 - the last world exposition of the twentieth century.

Special Session on ‘Differential Geometric Methods in Signal Processing’ integrated in SPAWC2004



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